The present disclosure relates to a controller and a control method for an internal combustion engine that are configured to control an internal combustion engine that includes a catalyst, which purifies exhaust gas discharged from cylinders, fuel injection valves provided for the respective cylinders, a canister, which collects fuel vapor in the fuel tank, which stores fuel to be injected by the fuel injection valves, and an adjustment device, which adjusts the amount of fuel vapor trapped in the canister flowing into the intake passage.
For example, Japanese Laid-Open Patent Publication No. 2004-218541 discloses a controller that executes dither control. In the dither control, when there is a requirement for increase in the temperature of a catalyst device (catalyst), the air-fuel ratio is made richer than the stoichiometric air-fuel ratio in some cylinders, while the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio in the other cylinders, such that the air-fuel ratio of the exhaust gas flowing into the catalyst becomes a target air-fuel ratio.
Also, a type of controller for an internal combustion engine is known that executes purge control to return fuel vapor in the fuel tank, which stores fuel to be injected from the fuel injection valves, to the intake passage.
In the case of executing the dither control, the air-fuel ratio in the rich combustion cylinder and the air-fuel ratio in the lean combustion cylinder are differentiated from each other. Thus, as compared with a case in which the air-fuel ratios of all the cylinders are controlled to be the same, the air-fuel ratio is restricted from being set to a value resistant to deterioration of combustion. This is likely to degrade the combustion. On the other hand, when the purge control is executed, the fuel vapor is not necessarily distributed evenly to the cylinders. This can cause the air-fuel ratio in each cylinder to deviate from the target air-fuel ratio. Therefore, when the dither control is executed during execution of the purge control, the tendency of deterioration of the combustion due to the execution of the dither control may be promoted and made noticeable by the distribution unevenness of fuel vapor among the cylinders due to the purge control.